In 2013, Saeko and the other Osaka Assassins relocated their bureau to avoid Abstergo, but they later came under attack by the Onmoraki-Gumi, a branch of the yakuza. Several Assassins were killed, including Kenichi, but Saeko survived and led the Assassin survivors on a mission of revenge against the Onmoraki-Gumi, killing its leaders and then taking over the gang. Saeko began using the gang to blend her Assassins into Osaka.[1]

On 18 December, Saeko met with Gavin and his cell of Assassins, who had come to Osaka looking for the Assassins there, only to discover the destroyed bureau. She laughed upon seeing Gavin's injuries, which he had sustained in a misunderstanding with Kiyoshi Takakura, and told his cell that Gavin had always been troublesome. Saeko explained to him why she had taken over the Onmoraki-Gumi, reasoning that like the Assassins, the yakuza worked in the dark to serve the light and had a long history of helping the common people.[1]

Over the next two days, Saeko exchanged information with Gavin. She informed him that the recent struggles against Abstergo and the yakuza had weakened the Osaka Brotherhood and drained their resources, with Japan's restrictive gun laws making it difficult to stay armed against their enemies. Gavin provided her with weapons his cell had procured in the Philippines and gave her the contact information for a supplier there. In thanks, Saeko passed on to Gavin an Animus headset her Assassins had stolen from a local Abstergo facility, and expressed her fears that the Assassin–Templar War was about to enter a new stage.[2]

On 31 December, Saeko was invited on by Eric Cooper to go on a tour of the Altaïr II. She disliked the disorganized state of the ship, and informed Captain Susan Drayton that the Japanese believed in starting off the New Year on a clean slate, which included having a clean house. Saeko enlisted the help of Susan and Eric in cleaning the ship and made homemade toshikoshi soba for them afterwards.[3]

By 26 March, Saeko was informed of the destruction of the Russian Brotherhood, and arranged to send weapons via the Philippine gun suppliers to a new cell of Assassins being set up in the country by the Georgian Assassins.[4]

By late 2015, Saeko organized two search teams to go to the Koreas and China, hoping to find Álvaro Gramática's secret laboratory and to help the local cells.[5]